1. Field of the Invention
The present invention relates to a touch panel system, and more particularly, to a touch panel system for a liquid crystal display (LCD) device.
2. Discussion of the Related Art
Presently, liquid crystal display (LCD) devices are commonly used because of their ability to produce high quality images, as well as their thin profile, light weight, and low power consumption. Liquid crystal module (LCM) devices are used for displaying video signals input from external sources, such as LCD panels, and commonly include polarizing plates, power sources, such as backlight devices, and light-guiding plates. The LCD panels include upper and lower glass substrates, and liquid crystal material injected between the upper and lower glass substrates. In addition, the polarizing plates are formed on lower and upper surfaces of the LCD panel for polarizing light irradiated onto the LCD panel using the backlight device. Moreover, a printed circuit board (PCB) is provided below a main support at a rear of the LCM device, and a drive integrated circuit (D-IC) is provided on the PCB to drive switching devices (i.e., thin film transistors) of the LCM device. Accordingly, the LCM device is electrically connected to the PCB using a tape carrier package (TCP) so that the video signals of the D-IC are transmitted to the LCM device. Furthermore, a digitizer is provided in the LCD device to display images on a screen and to input electric graphic image signals thereon. The digitizer is commonly referred to as an electric graphic input panel (EGIP) or a touch panel. Due to rapid development of LCD technology, it is possible to perform graphic image work that requires high resolution on the LCD device, whereby the digitizer is used as an input device of a notebook computer.
FIG. 1 is a schematic cross sectional view of a touch panel according to the related art. In FIG. 1, transparent ITO electrodes 3 and 4 are formed on opposing surfaces of two polyethylene terephtalate (PET) films 1 and 2 at a predetermined interval, wherein the two PET films 1 and 2 are bonded to each other using an insulating adhesive. Subsequently, a polyvinyl alcohol (PVA) film 5 is formed below the lower PET film 2 for polarizing light, and a triacetyl cellulose (TAC) film is formed below the PVA film 5 for protecting the PVA film 5 from humidity. In addition, a silver (A/G) layer is formed on the upper PET film 1.
An operation of the touch panel, which is categorized as a 4-line resistive-type touch panel, includes supplying a voltage to one transparent electrode along an X-axis direction, and supplying a voltage to another transparent electrode along a Y-axis direction. For example, a voltage is supplied to an upper transparent electrode 3 along the X-axis direction, and a voltage is supplied to a lower transparent electrode 4 along the Y-axis direction. Accordingly, signals are respectively supplied to the X-axis and the Y-axis in order to detect a location of a touching point in order to read the signals twice. For example, when the voltage is supplied to the upper transparent electrode 3 along the X-axis direction, the upper and lower transparent electrodes 3 and 4 contact each other at a predetermined portion, and a voltage value of the X-axis location is read through the lower transparent electrode 4. Similarly, when the voltage is supplied to the lower transparent electrode 4 along the Y-axis direction, the upper and lower transparent electrodes 3 and 4 contact each other at a predetermined portion, and a voltage value of the Y-axis location is read through the upper transparent electrode 3. Accordingly, the upper and lower transparent electrodes 3 and 4 have predetermined resistance values, so that the voltage value varies in accordance with a contact location of the upper and lower transparent electrodes 3 and 4. Thus, X-axis and Y-axis voltage values are input to a controller, whereby the controller detects coordinates of the touching point according to the X-axis and the Y-axis values.
When a predetermined portion of the upper substrate is touched with a finger or a pen, the upper and lower transparent electrodes 3 and 4 contact each other at the predetermined portion. Accordingly, the voltage values, which vary by the resistance value of the touching point, is output. For example, in order to read the voltage values that vary by the resistance value of the touching point, electrodes and lines for supplying the voltage to the upper and lower transparent electrodes 3 and 4 is necessary in order to read the voltage values.
FIG. 2 is a plan view of a connection structure between an extension of a touch panel and a controller according to the related art. In FIG. 2, a touch panel 9 includes two silver (A/G) electrodes 12 formed along left and right sides of an upper PET film 1 along the X-axis direction, and two A/G electrodes 11 formed along upper and lower sides of a lower PET film 2 along the Y-axis direction. Accordingly, the A/G electrodes 11 and 12 are formed within a dead space region of 2 μm to 3 μm along one direction of the touch panel 9. Moreover, a size of the touch panel 9 corresponds to sizes of an upper substrate of the LCD panel, wherein electrode lines of the touch panel 9 are formed in a 4-line resistive-type configuration.
In order to operate the 4-line resistive-type touch panel, interconnect of the touch panel 9, a touch controller 23, and a computer (i.e., CPU) using signal lines is required. A device in which the touch panel 9 and the touch controller 23 are connected to each other is referred to as a touch screen assembly. The touch controller 23 switches voltages and output signals provided to the upper and lower substrates of the touch panel 9, and receives input location information as electric signals. Then, the touch controller 23 converts the electric signal from analog signals to digital data, and transmits the digital data to the computer. Accordingly, the touch controller 23 is positioned separately from the LCD device, which is integrated with the touch panel, i.e, the touch controller 23 is positioned outside of the LCD device.
With the creation of ever smaller LCD devices having thin profiles and light weight to improve portability, integration of the LCD device with the touch controller is desired. For example, the touch controller can be mounted inside the LCD device, and the touch controller may be provided as a chip-type device positioned at rear of the LCM device.
In FIG. 2, the A/G electrodes 11 and 12 and conductive lines 13a, 13b, 13c, and 13d transmit and read the electric signals, and are formed within the dead space region of the touch panel 9. In addition, an extension of one of four sides of the touch panel 9 provides a connection part 15 that include end portions of the conductive lines 13a, 13b, 13c, and 13d. A flexible printed circuit board (FPCB) 16 is connected to the end portions of the conductive lines 13a, 13b, 13c, and 13d at the connection part 15. The FPCB 16 is used for electrically connecting the conductive lines 13a, 13b, 13c, and 13d of the A/G electrodes 11 and 12 of the touch panel 9 to the touch controller 23.
When the FPCB 16 of the touch panel 9 is connected to the touch controller 23, an FPCB connector 20 is mounted within the controller 23 so that a connection part 17 of the FPCB 16 is inserted into the FPCB connector 20, thereby electrically interconnecting the A/G electrodes 11 and 12 of the touch panel 9 to the touch controller 23. Since the FPCB 16 is formed of soft material(s), a stiffener is provided with the connection part 17 of the FPCB 16 for easy insertion of the connection part 17 of the FPCB 16 to the FPCB connector 20. Accordingly, the signals output from the 4-line electrodes (A/G electrodes 11 and 12) of the touch panel 9 are transmitted to the touch controller 23 using the FPCB 16 that is inserted into the FPCB connector 20 of the touch controller 23, thereby electrically interconnecting the touch panel 9 to the touch controller 23.
However, the signal connection structure between the touch panel and the touch controller according to the present invention has the following disadvantages. First, since the FPCB 16 of the touch panel 9 is electrically connected to the touch controller 23 by the FPCB connector 20, the FPCB connector 20 is thicker than IC chips below the LCM, whereby a total thickness of the entire interconnection system becomes thick. Thus, obtaining a thin profile and light weight of the LCD device is not achieved. Second, in order to connect the FPCB 16 of the touch panel 9 to the touch controller 23, the FPCB connector 20 is required, thereby increasing manufacturing costs. Third, when connecting the signal lines of the FPCB 16 to the FPCB connector 20, a connection failure may be generated.